In numerous fields it is necessary to record the temperature variations to which a product is subjected, e.g. in cases where, depending on circumstances, one or more variations or the overstepping of predetermined temperatures could make the product unsuitable for subsequent use.
One common example relates to the field of foodstuffs, where it is necessary to check continuously the quality of the cold of perishable produce: fresh, deep-frozen and frozen products, or foods which must be kept at a certain temperature.
It is however not exceptional for such products, in the course of the various manipulations to which they are subjected, to exceed a predetermined temperature above which they may be damaged.
It is also important to check continuously the quality of the cold supplied by equipment producing or maintaining cold, such as refrigerators or freezers, since an operating fault may result in a rise in temperature injurious to the products contained in them.
It is also necessary to maintain a continuous quality check on sterilization processes, in respect of both the products sterilized and the sterilization equipment.
Where health is concerned, it is necessary to maintain a continuous check on the conditions of prevation of blood or products derived from blood, biological and biogenetic products or certain pharmaceutical products for which temperatures must be strictly respected.
In the medical field, it is also necessary to maintain a continuous check on transplant organs and animal and human gametes.
In the industrial field, it is also desirable to monitor the operating temperature of certain machine parts, the manufacturing temperature of certain components, particularly electronic components, and also the storage temperature of various materials, such as composite materials or photographic emulsions, for example.
In addition, in the industrial field, temperature variations are in certain cases accompanied by variations of pressure which it is necessary to check continuously; for example pressure pipes monitored with the aid of instrumented valves.
It is therefore important to have available a simple, reliable device capable of being attached to the product and/or machines and of indicating by direct reading the overstepping of a determined temperature.
French Patent No. 2 560 992 in the name of the Applicant relates to a device in which the overstepping of a determined temperature is indicated by an irreversible coloration triggered with the aid of an element made of an alloy which memorizes its shape.